Data management in RAID environment

ABSTRACT

A data storage system includes a plurality of Data Storage Devices (DSDs) having a total storage capacity available for storing user data among the plurality of DSDs. Each DSD of the plurality of DSDs has a DSD storage capacity that contributes to the total storage capacity of the plurality of DSDs. A strip size is assigned to each DSD of the plurality of DSDs based at least in part on a portion of the total storage capacity that is contributed by the DSD storage capacity of the respective DSD. Data is received for storage in a data stripe across the plurality of DSDs and the data stripe is stored across the plurality of DSDs such that each DSD of the plurality of DSDs stores a different portion of the data stripe having the strip size assigned to the DSD.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/047,581, filed on Sep. 8, 2014, which is hereby incorporated by reference in its entirety. This application also claims the benefit of U.S. Provisional Application No. 62/059,671, filed on Oct. 3, 2014, which is hereby incorporated by reference in its entirety.

BACKGROUND

Data Storage Devices (DSDs) are often used to record data onto or to reproduce data from storage media. DSDs can include different types of storage media, such as solid-state memory (e.g., flash memory) or a rotating magnetic disk. With the increased need for data storage, more data is being stored in data storage systems including multiple DSDs rather than a single DSD.

One example of a data storage system with multiple DSDs can include a Redundant Array of Independent Disks (RAID) where data is stored across multiple DSDs. In such systems, data can be stored in a data stripe across the DSDs with each DSD including a portion of the data stripe in what is referred to as a data strip.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the embodiments of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the disclosure and not to limit the scope of what is claimed.

FIG. 1 is a block diagram depicting a data storage system including Data Storage Devices (DSDs) arranged as a Redundant Array of Independent Disks (RAID) according to an embodiment.

FIG. 2 is a block diagram depicting a DSD of FIG. 1 according to an embodiment.

FIG. 3 is a conceptual diagram providing an example of a static strip size for each DSD according to an embodiment.

FIG. 4 is a conceptual diagram providing an example of a varying strip size for each DSD according to an embodiment.

FIG. 5A is a table illustrating the assignment of varying strip sizes to different DSDs according to an embodiment.

FIG. 5B is an example of a stripe table indicating starting addresses for different portions of data stripes from the table of FIG. 5A according to an embodiment.

FIG. 6 is a conceptual diagram providing another example of a varying strip size for each DSD according to an embodiment.

FIG. 7 is a flowchart for a data stripe storage process according to an embodiment.

FIG. 8 is a conceptual diagram providing an example mirroring arrangement according to an embodiment.

FIG. 9 is a flowchart for a read process for a data storage system with mirroring according to an embodiment.

FIG. 10 is a flowchart for a write process for a data storage system with mirroring according to an embodiment.

FIG. 11 is a conceptual diagram providing an example of a data storage system including DSDs with varying data storage capacities according to an embodiment.

FIG. 12 is a flowchart for a data stripe storage process for DSDs with varying data storage capacities according to an embodiment.

FIG. 13 is a table illustrating the determination of different weights for different DSDs according to an embodiment.

FIG. 14 is a flowchart for a DSD replacement process according to an embodiment.

FIG. 15 is a flowchart for a DSD addition process according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth to provide a full understanding of the present disclosure. It will be apparent, however, to one of ordinary skill in the art that the various embodiments disclosed may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the various embodiments.

Overview of Example System Environment

FIG. 1 is a block diagram depicting data storage system 100 including Data Storage Devices (DSDs) 102, 104, 106, 108, and 110 arranged as a Redundant Array of Independent Disks (RAID) according to an embodiment. Each of DSDs 102, 104, 106, 108, and 110 can include storage media such as rotating magnetic disks and/or solid-state memory for storing data.

Data storage system 100 is in communication with host 200 which can use data storage system 100 as, for example, a data center storage system or a cloud-based storage system. In this regard, data storage system 100 may be a stand-alone system or part of a network such as a local area network, wide area network, or the Internet.

As shown in FIG. 1, data storage system 100 includes RAID controller 101, which allocates data among DSDs 102, 104, 106, 108, and 110. RAID controller 101 interfaces with DSDs 102, 104, 106, 108, and 110 via DSD interface 105, which may interface according to a standard such as, for example, Peripheral Component Interconnect Express (PCIe), Serial Advanced Technology Attachment (SATA), Small Computer System Interface (SCSI), or Serial Attached SCSI (SAS).

RAID controller 101 also interfaces with host 200 via host interface 103, which may interface with host 200 according to a standard such as, for example, Ethernet. RAID controller 101 and host 200 may be remotely located from each other via a network. Similarly, RAID controller 101 and one or more of DSDs 102, 104, 106, 108, and 110 need not be physically in the same location. For example, one or more of DSDs 102, 104, 106, 108, and 110 can be located in a different room, building, or city than other DSDs or RAID controller 101.

Those of ordinary skill in the art will appreciate that data storage system 100 can include more or less than those components shown in FIG. 1 and that the disclosed processes can be implemented in other environments.

In the example environment of FIG. 1, RAID controller 101 includes processor 107 which can be implemented using one or more processors for executing instructions such as a microcontroller, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), hard-wired logic, analog circuitry and/or a combination thereof. A processor of RAID controller 101 as referenced hereinafter can be one or more of the foregoing processors or another processor configured to perform functions described herein.

RAID controller 101 also includes memory 109 that can comprise a computer readable medium of various types of volatile or non-volatile Random Access Memory (RAM) that provide information stored in memory 109 to processor 107 during execution of instructions in software programs such as RAID application 10. Memory 109 also stores data that is used by processor 107 such as stripe table 12 and strip sizes 13.

RAID application 10 configures RAID controller 101 to communicate with each of DSDs 102, 104, 106, 108, and 110 to direct the storage of data among the DSDs and to access data from the DSDs. As will be appreciated by those of ordinary skill in the art, RAID controller 101 may use a particular storage scheme or RAID level (e.g., RAID 0, 1, 5, 6, 10) in determining which data to store on which DSD. The various storage schemes may provide for data redundancy and/or improved performance in accessing data from system 100.

Stripe table 12 provides location information for data stripes that are stored across the DSDs. A data stripe includes data that has been divided into portions that are stored in different DSDs. In one implementation, stripe table 12 can include logical addresses (e.g., Logical Block Addresses (LBAs)) indicating a starting location for the portions of data stripes stored across the DSDs. An example of stripe table 12 is discussed in more detail below with reference to FIG. 5B.

Strip sizes 13 provide the data sizes assigned to each DSD for the portions of the data stripes that are stored across the DSDs. As discussed in more detail below, the present disclosure allows the strip size or portion size assigned to each DSD to vary.

FIG. 2 is a block diagram depicting an example of DSD 106 of FIG. 1 according to an embodiment. In the embodiment of FIG. 2, DSD 106 is a Solid-State Hybrid Drive (SSHD) with a first storage media including magnetic recording media (e.g., disks in disk pack 150) and a second storage media including a solid-state media (e.g., solid-state memory 128). In other embodiments, each of disk pack 150 or solid-state memory 128 may be replaced by multiple HDDs or multiple Solid-State Drives (SSDs), respectively, so that DSD 106 includes pools of HDDs and/or SSDs. In addition, DSD 106 in other embodiments can include different types of recording media or may only include solid-state memory 128 or disk pack 150.

While the description herein refers to solid-state memory generally, it is understood that solid-state memory may comprise one or more of various types of memory devices such as flash integrated circuits, Chalcogenide RAM (C-RAM), Phase Change Memory (PC-RAM or PRAM), Programmable Metallization Cell RAM (PMC-RAM or PMCm), Ovonic Unified Memory (OUM), Resistive RAM (RRAM), NAND memory (e.g., single-level cell (SLC) memory, multi-level cell (MLC) memory, or any combination thereof), NOR memory, EEPROM, Ferroelectric Memory (FeRAM), Magnetoresistive RAM (MRAM), other discrete NVM (non-volatile memory) chips, or any combination thereof.

DSD 106 includes DSD controller 120 which includes circuitry such as one or more processors for executing instructions and can include a microcontroller, a DSP, an ASIC, an FPGA, hard-wired logic, analog circuitry and/or a combination thereof. In one implementation, DSD controller 120 can include a system on a chip (SoC). In one embodiment, an SSD controller may be utilized that operates in conjunction with DSD controller 120 for controlling operation of solid-state memory 128.

Host interface 126 is configured to interface DSD 106 with RAID controller 101 and may interface according to a standard such as, for example, PCIe, SATA, or SAS. In a non-RAID environment, DSD 106 may communicate with a host, such as a host computer, instead of RAID controller 101 using host interface 126. As will be appreciated by those of ordinary skill in the art, host interface 126 can be included as part of controller 120. Although FIGS. 1 and 2 depict the co-location of RAID controller 101 and DSD 106, in other embodiments the two need not be physically co-located. In such embodiments, DSD 106 may be located remotely from RAID controller 101 and connected to RAID controller 101 via a network interface.

In the example of FIG. 2, the first memory of DSD 106 includes rotating magnetic disks arranged in disk pack 150 which is rotated by a spindle motor (not shown). DSD 106 also includes Head Stack Assembly (HSA) 136 connected to the distal end of actuator 130 which is rotated by Voice Coil Motor (VCM) 132 to position HSA 136 in relation to disk pack 150. DSD controller 120 can include servo control circuitry (not shown) to control the position of HSA 136 and the rotation of disk pack 150 using VCM control signal 30 and SM control signal 33, respectively.

Disk pack 150 comprises multiple disks that are radially aligned or stacked so as to rotate about a spindle motor. Each disk in disk pack 150 includes a number of radially spaced, concentric tracks 152 for storing data. As shown in FIG. 2, each disk surface in disk pack 150 has an Outer Diameter (OD) portion, a Middle Diameter (MD) portion, and an Inner Diameter (ID) portion. HSA 136 includes multiple heads each arranged to read data from and write data to a corresponding surface of a disk in disk pack 150.

In some implementations, some or all of tracks 152 may overlap as a result of Shingled Magnetic Recording (SMR). SMR can provide a way of increasing the amount of data that can be stored in a given area on a disk by increasing the number of Tracks Per Inch (TPI). SMR increases TPI by using a relatively wide shingle write head in HSA 136 to overlap tracks like roof shingles. The non-overlapping portion then serves as a narrow track that can be read by a narrower read head. In other implementations, tracks 152 may be written using Conventional Magnetic Recording (CMR) such that the tracks do not overlap.

In the example of FIG. 2, DSD 106 also includes memory 140. In some implementations, memory 140 can be a volatile memory such as Dynamic Random Access Memory (DRAM) with a copy of DSD firmware 14 stored in a Non-Volatile Memory (NVM) such as in disk pack 150 or solid-state memory 128. Data stored in memory 140 can include data read from NVMs (which may include disk pack 150 and solid-state memory 128), data to be written to NVMs, instructions loaded from DSD firmware 14 for execution by DSD controller 120, and/or data used in executing DSD firmware 14. In this regard, DSD controller 120 can execute DSD firmware 14 to control operation of DSD 106.

In operation, host interface 126 receives read and write commands from a host or from RAID controller 101 via host interface 126 for reading data from and writing data to NVMs such as disk pack 150 and solid-state memory 128. In response to a write command, DSD controller 120 may buffer the data to be written in memory 140.

For data to be written to disk pack 150, a read/write channel (not shown) of DSD controller 120 may then encode the buffered data into write signal 32 which is provided to a head of HSA 136 for magnetically writing data to a disk surface of disk pack 150.

In response to a read command for data stored on a disk surface of disk pack 150, DSD controller 120 controls a head of HSA 136 to magnetically read data stored on the disk surface and to send the read data as read signal 32. A read/write channel of DSD controller 120 can then decode and buffer the data in memory 140 for transmission to a host or to RAID controller 101 via host interface 126.

For data to be stored in solid-state memory 128, DSD controller 120 receives data from host interface 126 and may buffer the data in memory 140. In one implementation, the data is then encoded into charge values for charging cells (not shown) of solid-state memory 128 to store the data.

In response to a read command for data stored in solid-state memory 128, DSD controller 120 in one implementation reads current values for cells in solid-state memory 128 and decodes the current values into data that can be transferred or copied to a host or to RAID controller 101. Such data may be buffered by DSD controller 120 before transferring or copying the data to a host or to RAID controller 101 via host interface 126.

Data Striping Examples for Improved Throughput

FIG. 3 is a conceptual diagram providing an example of a static strip size for each DSD in a speed banded arrangement according to an embodiment. In the example of FIG. 3, each DSD stores an equally sized portion or data strip of a data stripe. As shown at the bottom of FIG. 3, each DSD stores a 64 KB portion of a data stripe for a total data stripe width or size of 320 KB (i.e., 64 KB×5 DSDs).

The 64 KB portions or strips are stored in a speed banded arrangement across the DSDs so that the different data stripes stored across the DSDs can be accessed in approximately the same amount of time. The ability to access data stripes in approximately the same amount of time can allow for a more constant throughput which can be useful for certain applications such as video or other streaming applications. In such cases, a more consistent throughput also allows better tuning of other factors in a system such as buffer sizes, signaling, or timeouts.

Due to the varying track circumferences across a disk radius, tracks that are located in an OD portion of a disk surface are longer than tracks located in an ID portion of the disk surface. This results in a faster data transfer rate for tracks located toward the OD than for tracks located toward the ID since the time for the disk to complete one revolution of the disk is the same for all of tracks on the disk surface. To accomplish a more consistent throughput or data transfer rate for different data stripes, the 64 KB strips in FIG. 3 are located in different radial portions on the disk surfaces of the DSDs in what are referred to as speed bands that balance the varying data transfer rates of the different disk locations.

In addition, since the radial locations for the portions of a particular data stripe follow a pattern across the DSDs, each portion of the data stripe is accessed in the same radial direction (i.e., OD toward ID or ID toward OD) in the speed bands. By arranging the radial locations of access so that they progress in the same radial direction, it is ordinarily possible to more efficiently access data across the DSDs by reducing the amount of reverse seeking in an opposite radial direction. This uniform direction of access can also better take advantage of a track skew so that data can be read quicker when moving from one track to the next in the same radial direction. Such track skews circumferentially offset the beginning locations of adjacent tracks to account for the time it takes a head to travel from one track to the next so as to not miss the start of the next track in the adjacent track.

In the example of FIG. 3, DSDs 102, 104, 106, 108, and 110 store five data stripes with a first data stripe including portions or data strips A0, B0, C0, D0, and E0. A second data stripe includes portions A1, B1, C1, D1, and E1, and a third data stripe includes portions A2, B2, C2, D2, and E2. A fourth data stripe includes portions A3, B3, C3, D3, and E3, and a fifth data stripe includes portions A4, B4, C4, D4, and E4. In other implementations, data storage system 100 can store a different number of data stripes such as 100 data stripes rather than five data stripes.

Each data stripe in FIG. 3 is arranged to have different radial locations for its portions stored on different DSDs from an OD portion toward an ID portion. As a result, the overall time to access each of the data stripes is approximately the same since the different data transfer rates are balanced by storing the portions for each data stripe at different radial locations. The radial locations of access in the DSDs are shown in FIG. 3 as progressing in the same radial direction (e.g., from an OD location toward an ID location) with the arrows in FIG. 3 for the first data stripe going from A0 in DSD 102 toward E0 in DSD 110.

The left side of FIG. 3 provides the data transfer rates in MB/s for each radial location with 175 MB/s for the OD portion to 90 MB/s for the ID portion. The total data transfer rate for the data stripe is the sum of the data transfer rates for the individual DSDs, or 450 MB/s. Using a fixed strip size of 64 KB, the time for accessing the 64 KB data strip by location is provided to the right of the data transfer rates. As shown in FIG. 3, the fastest access time is at the OD portion with 0.37 ms and the slowest access time is at the ID portion with 0.71 ms. Since the DSDs can operate in parallel, the overall access time for the data stripes of FIG. 3 is therefore the slowest time to access a data strip, or 0.71 ms. Although the arrangement of FIG. 3 allows for a more constant throughput of data, the arrangement of FIG. 4 discussed below increases the overall data transfer rate for the data stripes by varying the strip sizes based on the radial location of the data strip.

The example of FIG. 4 is similar to the example of FIG. 3 in that the data stripes are speed banded by storing portions of the data stripes at different radial locations across the DSDs. In addition, each portion of the data stripe is arranged in a radial location so that when the data stripe is accessed, the radial locations of access in the DSDs progress in the same radial direction as in the example of FIG. 3. However, the arrangement of FIG. 4 differs from that of FIG. 3 in that the sizes of each portion or data strip within the data stripe vary depending on the radial location.

As shown in FIG. 4, the amount of data transferred for each DSD (i.e., the strip size) varies from 64 KB for an ID portion of the data stripe to 124 KB for an OD portion of the data stripe. In the case of the first data stripe including portions A0, B0, C0, D0, and E0, the OD diameter portion A0 has a strip size of 124 KB and the ID portion E0 has a strip size of 64 KB. As a result of these varying strip sizes, the time to access the data strips is approximately the same for each of the DSDs, which is the slowest time from the example of FIG. 3 of 0.71 ms. In other words, the strip size is set for each portion based on its radial location so that each portion can be completely read by its respective DSD in approximately the same amount of time.

The overall amount of data transferred for the data stripe is then increased from the example of FIG. 3 due to the larger data strips located away from the ID location. Since the total access time for the data stripe is still limited by the slowest access time of 0.71 ms, the total data transfer rate is increased because more data is transferred in the same amount of time. In this regard, the total data transfer rate in FIG. 4 has increased to 664 MB/s from 450 MB/s in FIG. 3. In addition, the total size or width of the data stripe has increased to 470 KB in FIG. 4 from a stripe width of 320 KB in FIG. 3.

FIG. 5A is a table illustrating the assignment of varying strip sizes to different DSDs as shown in FIG. 4. In the example of FIG. 5A, each of data stripes 0, 1, 2, 3, and 4 include a 124 KB strip, a 109 KB strip, a 94 KB strip, a 79 KB strip, and a 64 KB strip to form a combined data stripe of 470 KB. These varying strip sizes are staggered across the DSDs or offset from one DSD to the next based on the radial locations of access progressing in the same radial direction across the DSDs.

Although the strip sizes making up the data stripes vary in the example of FIGS. 4 and 5A, the overall size or stripe width of the data stripes remain the same at 470 KB. This can facilitate a consistent throughput or data transfer rate among the different data stripes while increasing the data transfer rate when compared to data stripes that have a static or fixed strip size.

FIG. 5B is an example of stripe table 12 that is stored in memory 109 of RAID controller 101 according to an embodiment. Stripe table 12 can include at least one address for each portion of a data stripe to identify the portion and to associate the portion with the DSD storing the portion. In some implementations, processor 107 can set up stripe table 12 when executing RAID application 10 during an initialization process of data storage system 100. In such an implementation, the addresses used in stripe table 12 can be based on information collected from the DSDs concerning the addresses available for storing data strips. Processor 107 of RAID controller 101 can then use stripe table 12 when writing or reading data stripes stored across the DSDs of data storage system 100.

In the example of FIG. 5B, stripe table 12 indicates starting addresses in terms of a starting LBA for different portions of data stripes from the table of FIG. 5A. Other embodiments may use different information for identifying data strips such as an address range for a particular data strip or another indication of which DSD stores the data strip.

In FIG. 5B, a starting address for a strip is calculated by multiplying a previous strip size by a sector size of 1,024 bytes and adding the result to the starting address for the previous data strip. For example, the starting address for the data strip stored on DSD 104 for data stripe 0 is calculated by multiplying 1,024 bytes by the previous strip size for DSD 102 of 124 KB and adding this product to a starting address of 0 for the previous data strip. This calculation is similar for each strip in the data stripe. Other implementations may use a different calculation for determining a starting address for a data strip, such as using a sector size other than 1,024 bytes.

The end LBA column in FIG. 5B is not part of stripe table 12, but is provided for illustration purposes to more clearly show the incrementing of the addresses for the start of the next data stripe stored on DSD 102. In this regard, the starting address for each data stripe indicates a beginning location of the data stripe. The starting addresses for each data stripe after the first data stripe 0 are offset from the starting address of the previous data stripe by a predetermined address offset that is based on the number of data stripes stored across the DSDs.

In the example of FIG. 5B, the address offset is 481,281 such that the beginning location of each data stripe is offset from the beginning location of the previous data stripe by 481,281. This offset is determined by dividing the total number of addresses available for the data stripes by the number of data stripes and multiplying this result by a drive ID or drive number. In the example of FIG. 5B, the offset is determined by dividing the total number of 2,406,403 LBAs by five data stripes to yield 481,281 when rounded to the nearest whole number. The starting address of each data stripe on DSD 102 is then determined by adding this offset to the starting address of the previous data stripe. As appreciated by those of ordinary skill in the art, the specific addresses or ways of determining starting addresses may differ in other implementations.

Although the data stripes of FIG. 5B all start on DSD 102, other implementations may include data stripes that start on different DSDs. In one such example, data stripe 0 may start on DSD 102 while data stripe 1 starts on DSD 104. Despite starting on different DSDs, each of the data stripes in such an example would be the same overall size and have approximately the same data transfer rate since the sizes of the data strips making up each data stripe would vary across the DSDs depending on the radial locations of the data strips.

FIG. 6 provides another example of a varying strip size for each DSD according to an embodiment. Unlike the example of FIG. 4, the first data stripe in FIG. 6 does not begin at an OD location. As shown in FIG. 4, the first data stripe including data strips A0, B0, C0, D0, and E0, begins on DSD 102 at a radial location closer to an ID location than to an OD location. The next data strip in the first data stripe is indicated with an arrow to B0 which is stored on DSD 104 at an ID location. The first data stripe continues with data strip C0 stored on DSD 106 at an OD location and proceeds to D0 on DSD 108 and to E0 on DSD 110.

As with the data stripes of FIG. 4, the data stripes of FIG. 6 each have the same mix of different sized data strips for different radial locations. As a result, the data transfer rates for each data stripe are generally the same at 664 MB/s with the same total stripe width of 470 KB.

FIG. 7 is a flowchart for a data stripe storage process that can be performed by processor 107 of RAID controller 101 by executing RAID application 10 according to an embodiment. Block 702 can be performed by processor 107 in an implementation where mirroring is used to store a copy of data stored on a mirrored DSD. In implementations where mirroring is not used, block 702 may be omitted.

FIG. 8 provides an example mirroring arrangement based on the example of FIG. 4. As shown in FIG. 8, a first data stripe includes data strips A0, B0, C0, D0, and E0 stored on DSDs 102, 104, 106, 108, and 110, respectively. A copy of each of these data strips is stored on DSDs 302, 304, 306, 308, and 310, respectively. Each of the copies of the data strips are stored at approximately the same radial location as where the original data strip is stored on the mirrored DSD. For example, if portion A0 is stored at an OD location of DSD 102 as shown in FIG. 8, a copy of A0 is also stored at an OD location of DSD 302 to provide for the same data transfer rate.

In addition to providing for redundancy, a mirroring arrangement can also ordinarily improve system performance in performing read and write commands as discussed in more detail below with reference to the processes of FIGS. 9 and 10. In other embodiments, not all of the DSDs may be paired with another DSD. For example, in one embodiment, only DSDs having less than a certain threshold data storage capacity may be paired together for redundancy to reduce the impact on an overall storage capacity of the system when compared to mirroring each DSD in the system.

Returning to the process of FIG. 7, processor 107 in block 702 optionally determines a plurality of DSDs from a larger set of DSDs by pairing DSDs that have the closest storage capacity to each other. This can be performed as part of an initialization of data storage system 100 to set up a mirroring arrangement as shown in the example of FIG. 8. In pairing the DSDs for mirroring, the storage capacity that is considered is the storage capacity that is available for storing data strips. In some implementations, this may not include the full storage capacity of the DSD, but rather, only a storage capacity of the DSD that is available for storing data strips.

By pairing DSDs by similar storage capacity, it is ordinarily possible to make better use of the storage capacity available across data storage system 100 since the amount of data that can be stored on a particular DSD is generally limited by the smaller capacity of the mirrored DSD and the mirroring DSD where the copied data strips are stored.

In block 704, processor 107 receives data via host interface 103 for storage in a data stripe. In block 706, processor 107 determines strip sizes for each portion of the data stripe based on a radial location where the portion will be stored. In determining the strip sizes, processor 107 may use stripe table 12 which can provide starting addresses for the different data strips. As discussed above with reference to FIGS. 4 to 5B, the strip sizes will vary depending on the radial locations where the data strip is stored.

In block 708, processor 107 via DSD interface 105 stores the data stripe with each portion or data strip arranged in a radial location so that the radial locations of access progress in the same radial direction. As noted above, arranging the data strips in this way can ordinarily reduce the amount of reverse seeking in the opposite radial direction and take better advantage of a track skew where tracks are circumferentially offset so as not to miss the beginning of a next track as a head travels from one track to the next. In addition, each data strip of the data stripe has the size determined in block 706, which is based on its radial location. In implementations where DSDs are mirrored, processor 107 also stores a copy of the data strip on a mirroring DSD at approximately the same radial location where the original portion is stored on the mirrored DSD.

FIG. 9 is a flowchart for a read process for a data storage system with mirroring where the mirroring can be used to shorten the time for performing a read command to read a data strip. The process of FIG. 9 can be performed by processor 107 executing RAID application 10 according to an embodiment.

In block 902, processor 107 sends a first read command to access a portion of a data stripe from a mirrored DSD such as DSD 102 in FIG. 8. The read command sent in block 902 can form part of multiple read commands sent to each of DSDs 102, 104, 106, 108, and 110 to read a full data stripe.

In block 904, processor 107 sends a second read command to a mirroring DSD to access a copy of the portion requested in block 902. With reference to the example of FIG. 8, if the first read command is sent to DSD 102 for the original data strip A0, processor 107 can send a second read command to DSD 302 in block 904 to read the copy of data strip A0 stored on DSD 302.

In block 906, after waiting for a response from either the mirrored DSD (e.g., DSD 102) or the mirroring DSD (e.g., DSD 302), processor 107 receives a first response and determines whether the first response indicates successful completion of the read command. If so, data is received for the first response in block 908. In block 910, processor 107 determines whether the data strip was first received from the mirrored DSD (e.g., DSD 102) or whether the copy of the data strip was first received from the mirroring DSD (e.g., DSD 302). If the data strip was first received from the mirrored DSD, processor 107 aborts the second read command sent to the mirroring DSD in block 914. On the other hand, if the copy of the data strip was received first, processor 107 aborts the first read command sent to the mirrored DSD in block 912.

By sending read commands to each of the mirrored DSD and the mirroring DSD, it is ordinarily possible to shorten the time it takes to receive the requested portion. Even though the original portion and the copied portion are located in approximately the same radial location, the respective disks of the mirrored DSD and the mirroring DSD may be at different points in their rotation such that one of the two DSDs can read the requested data strip before the other. In some implementations, the spinning of the disks of the mirroring and mirrored DSDs may also be synchronized so that they are rotationally out of phase with each other by 180 degrees so that the requested data strip can be accessed by at least one of the DSDs within half a disk revolution.

Returning to FIG. 9, if the first received response in block 906 does not indicate successful completion of a read command, processor 107 in block 916 after determines whether a second received response in block 916 indicates successful completion of the other read command. If not, the process proceeds to block 920 to perform error handling for both the mirrored DSD and the mirroring DSD. Examples of such error handling can include, for example, a read retry or a media test for the DSD.

On the other hand, if processor 107 determines that the second received response in block 916 indicates successful completion of a read command, processor 107 in block 918 receives data for the second received response which can include the data strip or a copy of the data strip. The process then proceeds to block 920 to perform error handling for the DSD corresponding to the unsuccessful first response received in block 906.

By sending read commands to each of the mirrored DSD and the mirroring DSD, it is ordinarily possible to obtain the requested data strip despite an error in performing a read command at one of the mirrored DSD or the mirroring DSD. This redundancy reduces the likelihood that access to a data stripe will be hindered by an error in reading a portion of the data stripe. The error handling of block 920 for the DSD with the failed read command can then be performed as background activity.

FIG. 10 is a flowchart for a write process for a data storage system with mirroring where the mirroring can be used to shorten the time for indicating the completion of a write command to a host. By indicating the completion of a write command sooner, it may be possible to improve an overall system performance when the host may be waiting for the completion of the write command before proceeding to a next command or other action. The process of FIG. 10 can be performed by processor 107 executing RAID application 10 according to an embodiment.

In block 1002, processor 107 receives a request from host 200 via host interface 103 to store data in data storage system 100. The data can include data to be stored in a data stripe across the DSDs of data storage system 100.

In block 1004, processor 107 sends a first set of write commands via DSD interface 105 to store an original data stripe across mirrored DSDs in data storage system 100, such as DSDs 102, 104, 106, 108, and 110 in FIG. 8.

In block 1006, processor 107 sends a second set of write commands via DSD interface 105 to store a copy of the original data stripe across a set of mirroring DSDs, such as DSDs 302, 304, 306, 308, and 310 in FIG. 8. As in the example of FIG. 8, each of the mirroring DSDs is paired with a corresponding mirrored DSD to store a copy of data stored on the corresponding mirrored DSD.

In block 1008, processor 107 receives indications from the mirrored and mirroring DSDs indicating the storage of portions of the original data stripe or portions of the copy of the original data stripe. Each of the mirrored DSDs and the mirroring DSDs may send a notification such as a command completion indication back to RAID controller 101.

In block 1010, processor 107 sends a completion notification to host 200 indicating that the data has been stored upon initially receiving indications for each pair of mirroring DSDs and corresponding mirrored DSDs. Processor 107 may keep track in memory 109 of whether a notification has been received for each pair of DSDs and then send the completion notification to host 200 in block 1010 upon initially receiving notifications from all of the pairs of DSDs.

By sending a completion notification to host 200 upon initially receiving notifications for each pair of DSDs, it is ordinarily possible for processor 107 to send the completion notification to host 200 sooner than if processor 107 had to wait to receive all notifications from every mirrored and mirroring DSD. Even though the original portion and the copied portion are located in the same radial location, the respective disks of the mirrored DSD and the mirroring DSD may be at different points in their rotation such that one of the two DSDs can write its portion of the data stripe before the other. In some implementations, the spinning of the disks of the mirroring and mirrored DSDs may also be synchronized so that they are rotationally out of phase with each other by 180 degrees so that each data strip or its copy can be written in either the mirroring DSD or the mirrored DSD within half a disk revolution.

Variable Capacity Data Striping Examples

FIG. 11 is a conceptual diagram providing an example of a data storage system including DSDs with varying data storage capacities according to an embodiment. Oftentimes, DSDs will have slightly different actual data storage capacities due to variations during manufacturing even if the DSDs were intended to have the same data storage capacity. Using a fixed or static data strip size as in the example of FIG. 4, generally does not make full use of the actual data storage capacity on each DSD since all of the DSDs in such a configuration will be limited to the smallest data storage capacity among the DSDs.

The following embodiments therefore provide for data strips of varying size based on the amount of storage capacity contributed by the DSD storing the data strip to a total storage capacity of the data storage system. This arrangement ordinarily allows for a more efficient use of the total storage capacity of the DSDs.

As shown in the example of FIG. 11, data storage system 100 provides a total data storage capacity of 26.2 TB with DSD 102 contributing 5.1 TB, DSD 104 contributing 5.5 TB, DSD 106 contributing 4.9 TB, DSD 108 contributing 5.3 TB, and DSD 110 contributing 5.4 TB. The contribution amount of each DSD can be the entire storage capacity of the DSD, or in some cases, a portion of its storage capacity that has been made available for storing data strips. In the example of FIG. 11, a weight is determined for each DSD based on a percentage of the total storage capacity that is contributed by the DSD. As shown in FIG. 11, DSD 108 contributes the most with a weight of 20.9% and DSD 106 contributes the least with a weight of 18.7%. The storage capacity for the DSDs may be based on using different types of NVM media such as a rotating magnetic disk and/or a solid state memory.

The strip sizes assigned to each DSD are based at least in part on the portion of the total storage capacity that is contributed by the respective DSD's storage capacity. In the example of FIG. 11, a total stripe width of 512 KB is used and each DSD's strip size is the product of the DSD's weight and the total stripe width. For example, the strip size assigned to DSD 106 is its weight of 18.7% multiplied by the total stripe width of 512 KB to yield a strip size for DSD 106 of 96 KB. In other embodiments, the assigned strip size may be determined by also considering other factors in addition to its storage capacity contribution, such as a performance level of the DSD or a level of reliability of the DSD.

FIG. 12 is a flowchart for a data stripe storage process for DSDs with varying data storage capacities according to an embodiment. The process of FIG. 12 can be performed by processor 107 of RAID controller 101 executing RAID application 10 according to an embodiment.

Block 1202 can be performed by processor 107 in an implementation where mirroring is used to store a copy of data stored on a mirrored DSD. In implementations where mirroring is not used, block 1202 may be omitted. In block 1202, processor 107 optionally determines a plurality of DSDs from a larger set of DSDs by pairing DSDs that have the closest storage capacity to each other. This can be performed as part of an initialization of data storage system 100 to set up a mirroring arrangement as shown in the example of FIG. 8. In pairing the DSDs for mirroring, the storage capacity that is considered is the storage capacity that is available for storing data strips. In some implementations, this may not include the full storage capacity of the DSD, but rather, only a storage capacity of the DSD that is available for storing data strips.

By pairing DSDs with similar storage capacity, it is ordinarily possible to make better use of the storage capacity available across data storage system 100 since the amount of data that can be stored on a particular DSD is generally limited by the smaller capacity between the mirrored DSD and the mirroring DSD where the copied data strips are stored.

In block 1204, processor 107 optionally determines a weight for each DSD of the plurality of DSDs based on a percentage of the total storage capacity contributed by the DSD. As in the example of FIG. 11, the individual contribution of each DSD can be divided by a total storage capacity for all of the DSDs to determine the weight for each DSD. In other embodiments, the weight for each DSD may be determined differently such as by assigning predetermined weights for each DSD based on whether the contribution of the DSD falls within a certain storage capacity range.

In block 1206, processor 107 assigns a strip size to each DSD in data storage system 100 based at least in part on a portion of the total storage capacity contributed by the DSD storage capacity of the respective DSD. In an implementation where mirroring is used, processor 107 determines the contribution for each mirrored DSD using the storage capacity of its respective mirroring DSD if the storage capacity of the mirroring DSD is less than the storage capacity of the mirrored DSD.

The strip size can be based on a weight determined in block 1204 or can be assigned based on whether the storage capacity of the DSD exceeds a certain threshold. In one implementation, the strip size can be assigned based on whether the DSD's storage capacity is less than or greater than an average DSD storage capacity for the DSDs in data storage system 100. In some implementations, other factors such as a performance of a particular DSD or a reliability of the DSD may also be considered in assigning a strip size to the DSD. Processor 107 can establish or update the address ranges for stripe table 12 to reflect the strip sizes assigned to each DSD and/or store strip sizes for the DSDs in memory 109 as strip sizes 13.

In block 1208, processor 107 receives data via host interface 103 for storage in a data stripe across DSDs 102, 104, 106, and 108. The data is then stored in a data stripe in block 1210 with each DSD having the strip size assigned in block 1206. In storing the data, processor 107 may divide the received data into data strips using stripe table 12 or strip sizes 13 and send write commands for the data strips to the DSDs via DSD interface 105.

FIG. 13 is a table illustrating the determination of different weights for different DSDs as DSDs are removed, replaced, or added according to an embodiment. At an initial point in time represented by the first row in the table of FIG. 13, data storage system 100 includes five DSDs for storing data stripes. Each of the initial DSDs including DSDs 102, 104, 106, 108, and 110 are assigned a strip size based on their respective contributions to the total data storage capacity. The initial total data storage capacity is the sum of the storage capacities of DSDs 102, 104, 106, 108, and 110, or 26.2 TB. The weight shown in the first row of the table is then the storage capacity for that particular DSD divided by the total storage capacity of 26.2 TB.

In the second row, DSD 110 has been removed and is no longer available for storing new data stripes. In some cases, the removal of DSD 110 can be due to a failure of DSD 110. In other cases, the removal of DSD 110 can be due to DSD 110 reaching its capacity for storing data strips. The remaining DSDs (i.e., DSDs 102, 104, 106, and 108) are reassigned larger strip sizes to make up for the storage capacity lost by removing DSD 110. This is shown in the example of FIG. 13 with the recalculated weights for DSDs 102, 104, 106, and 108.

As shown in FIG. 13, the removal of DSD 110 occurs at a stripe crossover point of the third data stripe of data stripe 2. In a case where DSD 110 is to be completely removed from the system, the data from the first two data stripes (i.e., data stripes 0 and 1) can be redistributed or reorganized among the remaining DSDs using the new strip sizes assigned to the remaining DSDs. In a case where DSD 110 is still available for accessing data from the first two data stripes, such as when DSD 110 has reached its available data storage capacity, the first two data stripes can have the strip sizes corresponding to the first row weights. The data stripes following the first two data stripes would then have the new strip sizes shown in the second row after the stripe crossover point of the third data stripe of data stripe 2. After this point, the strip size assigned to DSD 110 in strip sizes 13 can be set to 0 so that no new data strips are stored on DSD 110 after the first stripe crossover point.

After the fourth data stripe (i.e., data stripe 3), a new DSD 112 is added to replace the lost capacity of DSD 110. In the example of FIG. 13, replacement DSD 112 has a larger storage capacity than replaced DSD 110 (5.6 TB versus the replaced storage capacity of 5.4 TB). A new strip size is assigned to each of DSDs 102, 104, 106, 108, and 112 reflecting the changes in total storage capacity and the relative contributions of each DSD to the total storage capacity. The new strip sizes can be added to strip sizes 13 for each of DSDs 102, 104, 106, 108, and 112.

In the fourth row, or at the stripe crossover point of the fifth data stripe 4, three new DSDs are added to data storage system 100 to increase the number of DSDs. The data stripes up to and including the stripe crossover point of data stripe 4 will have data strip sizes based on the previous weight or weights for the DSDs. After the third stripe crossover point, only the new DSDs 114, 116, and 118 are used for storing new data stripes. The strip sizes for the new DSDs are based on the new total storage capacity of the new DSDs their respective contributions to the new total storage capacity. Strip sizes 13 in memory 109 can be modified to add the strip sizes for the new DSDs and to set the strip sizes for the old DSDs to 0 after the third stripe crossover point of data stripe 4.

The use of the stripe crossover point allows for the old DSDs to continue to be used for the data stripes up to the stripe crossover point while adding new DSDs to data storage system 100. This can ordinarily allow for new DSDs to be added without having to rebuild or redistribute the data stripes before the stripe crossover point.

By dynamically adjusting the strip sizes, it is also possible to prolong the usable life of data storage system 100 by allowing for the replacement of DSDs that may have failed or reached their capacity without having to rebuild all of the data stripes, which can consume system resources and take a significant amount of time. The changes in the strip sizes over time can lead to different versions of stripe table 12 that are used depending on a data stripe's placement in relation to one or more stripe crossover points. In addition, and as discussed above, RAID controller 101 may store multiple strip sizes in strip sizes 13 for each DSD reflecting the strip sizes at different stripe crossover points.

FIG. 14 is a flowchart for a DSD replacement process according to an embodiment where the replacement DSD has a smaller DSD storage capacity than the DSD that was replaced and not all of the data strips stored on the replaced DSD fit onto the replacement DSD. In other situations where the available storage capacity on the replacement DSD is large enough to accommodate all of the data strips of the replaced DSD, the data stored on the replaced DSD can be copied from a mirroring DSD or from an external source onto the replacement DSD. In other embodiments, the largest DSD from a set of DSDs to be used in the system can be set aside or reserved as a replacement DSD to ensure that the replacement DSD can accommodate all of the data strips of a replaced DSD. In contrast, the process of FIG. 14 allows for the use of unused capacity on the remaining DSDs without having to add a replacement DSD with an equal or larger capacity than the replaced DSD.

The process of FIG. 14 can be performed by processor 107 executing RAID application 10 according to an embodiment. In block 1402, processor 107 determines a difference between the DSD storage capacity of the replaced DSD and the DSD storage capacity of the replacement DSD. For example, if the replaced DSD had a storage capacity of 5.4 TB and the replacement DSD has a storage capacity of 5.0 TB, the difference determined in block 1402 would be 0.4 TB.

In block 1404, processor 107 identifies incomplete data stripes due to the smaller storage capacity of the replacement DSD. In cases where the replacement DSD can store all of the data strips of the replaced DSD, there will be no incomplete data stripes and the process of FIG. 14 need not be performed.

In one implementation, processor 107 in block 1404 can identify the incomplete data stripes by dividing the difference in storage capacity determined in block 1402 by the data size used for each data stripe and then subtracting this value from the total number of data stripes stored in data storage system 100. This difference provides a stripe crossover point where any data stripes beyond the stripe crossover point will be incomplete due to the smaller size of the replacement DSD.

In block 1406, processor 107 optionally determines a replacement weight for the incomplete data stripes for each DSD other than the replaced DSD and the replacement DSD. The replacement weight is based on an increased percentage of a total replacement storage capacity equal to the sum of the storage capacities of the DSDs other than the replaced DSD and the replacement DSD.

In block 1410, the incomplete data stripes are stored across the DSDs other than the replaced DSD and the replacement DSD such that for each incomplete data stripe, each DSD stores a different replacement portion of the incomplete data stripe having the replacement strip size assigned to the DSD. In this way, it is ordinarily possible to use space available on other DSDs to store data strips of the incomplete data stripes. Processor 107 may assign the replacement DSD a strip size of 0 for data stripes after the stripe crossover point so that new data stripes are not stored on the replacement DSD, which will have reached its available storage capacity by storing data strips from the replaced DSD.

The process of FIG. 14 assumes that there is enough available space remaining on the other DSDs to store the incomplete data stripes and still provide for any workspace overhead that may be needed, such as for a file system. After the incomplete data stripes have been stored, the replacement strip sizes may also be used to store new data stripes across the DSDs other than the replaced DSD and the replacement DSD.

FIG. 15 is a flowchart for a DSD addition process according to an embodiment. The process of FIG. 15 can be used in cases where a replacement DSD has an available storage capacity greater than or equal to the available storage capacity of a replaced DSD or when increasing the number of DSDs in data storage system 100. In some embodiments, the process of FIG. 15 can be performed by processor 107 executing RAID application 10.

In block 1502, processor 107 optionally determines a new weight for each DSD based on a percentage of a new total storage capacity contributed by each DSD. In the case where a replacement DSD is replacing a replaced DSD, such as in the third row of FIG. 13, a new weight for each DSD can be determined by dividing the individual contribution of each DSD by the new total storage capacity (e.g., the sum of the storage capacities of DSDs 102, 104, 106, 108, and 112 in FIG. 13). In the case where one or more new DSDs are added to data storage system 100 to increase the number of DSDs, the available storage capacities of the new DSDs form the new total storage capacity and each of the new DSDs is assigned a new weight based on its contribution to the new total storage capacity. The old DSDs may then be assigned a new weight of 0 so that new data stripes (i.e., after a stripe crossover point) are not stored on the old DSDs.

In block 1504, processor 107 assigns a new strip size to each DSD based at least in part on a portion of the new total storage capacity contributed by the DSD. The strip size can be based on a weight determined in block 1504 or can be assigned based on whether the storage capacity of the DSD exceeds a certain threshold. In one implementation, the strip size can be assigned based on whether the DSD's storage capacity is less than or greater than an average DSD storage capacity for the DSDs in data storage system 100. In some implementations, other factors such as a performance of a particular DSD or a reliability of the DSD may also be considered in assigning a strip size to the DSD. Processor 107 can update the address ranges for stripe table 12 to reflect the new strip sizes assigned to each DSD in block 1504 and/or store the new strip sizes for each DSD in strip sizes 13 in memory 109.

In block 1506, processor 107 receives data via host interface 103 for storage in a new data stripe. In block 1508, processor 107 via DSD interface 105 stores the new data stripe such that each DSD stores a different portion of the new data stripe having the new strip size assigned to the DSD. As part of storing the new data stripe, processor 107 may use stripe table 12 which can provide starting addresses for the data strips of the new data stripe or may use the new strip sizes stored in strip sizes 13 for each DSD.

Other Embodiments

Those of ordinary skill in the art will appreciate that the various illustrative logical blocks, modules, and processes described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. Furthermore, the foregoing processes can be embodied on a computer readable medium which causes a processor or computer to perform or execute certain functions.

To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, and modules have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Those of ordinary skill in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

The various illustrative logical blocks, units, modules, and controllers described in connection with the examples disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The activities of a method or process described in connection with the examples disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The steps of the method or algorithm may also be performed in an alternate order from those provided in the examples. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable media, an optical media, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an Application Specific Integrated Circuit (ASIC).

The foregoing description of the disclosed example embodiments is provided to enable any person of ordinary skill in the art to make or use the embodiments in the present disclosure. Various modifications to these examples will be readily apparent to those of ordinary skill in the art, and the principles disclosed herein may be applied to other examples without departing from the spirit or scope of the present disclosure. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the disclosure is, therefore, indicated by the following claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

What is claimed is:
 1. A data storage system, comprising: a plurality of Data Storage Devices (DSDs) collectively having a total storage capacity available for storing user data among the plurality of DSDs with each DSD of the plurality of DSDs having a DSD storage capacity that contributes to the total storage capacity of the plurality of DSDs; and a controller configured to: determine a weight for each DSD of the plurality of DSDs based on a percentage of the total storage capacity that is contributed by the DSD storage capacity of the respective DSD; assign a strip size to each DSD of the plurality of DSDs based on the determined weight for the respective DSD, including: assign a first strip size to a first DSD of the plurality of DSDs based at least in part on a first DSD storage capacity contributed by the first DSD to the total storage capacity; and assign a second strip size to a second DSD of the plurality of DSDs based at least in part on a second DSD storage capacity contributed by the second DSD to the total storage capacity, wherein: the second DSD storage capacity contributed by the second DSD differs from the first DSD storage capacity contributed by the first DSD, and the second strip size assigned to the second DSD differs from the first strip size assigned to the first DSD; receive data for storage in a data stripe across the plurality of DSDs; and store the data stripe across the plurality of DSDs such that each DSD of the plurality of DSDs stores a different portion of the data stripe, wherein: the first DSD is configured to store a first portion of the data stripe having the first strip size, and the second DSD is configured to store a second portion of the data stripe having the second strip size.
 2. The data storage system of claim 1, wherein the controller is further configured to determine the plurality of DSDs from a larger set of DSDs by: pairing each of one or more DSDs of the larger set with another DSD of the larger set that has the closest DSD storage capacity available for storing user data; and for each pair of DSDs: setting a first DSD of the pair as a DSD of the plurality of DSDs; and setting the other DSD of the pair as a mirroring DSD for storing a copy of user data stored on the first DSD.
 3. The data storage system of claim 1, further comprising at least one mirroring DSD for storing a copy of data stored on a respective mirrored DSD of the plurality of DSDs, wherein the controller is further configured to determine the DSD storage capacity contribution for each mirrored DSD of the plurality of DSDs using a mirroring DSD storage capacity of the mirroring DSD responsive to the mirroring DSD storage capacity being less than the DSD storage capacity of the mirrored DSD.
 4. The data storage system of claim 1, wherein: the plurality of DSDs stores a plurality of data stripes across the plurality of DSDs; and the controller is further configured to, responsive to one of the plurality of DSDs being replaced by a replacement DSD having a DSD storage capacity less than the DSD storage capacity of the replaced DSD: determine a difference between the DSD storage capacity of the replaced DSD and the DSD storage capacity of the replacement DSD, wherein the total storage capacity is reduced to a total replacement storage capacity for storing user data among the plurality of DSDs other than the replaced DSD and the replacement DSD; identify incomplete data stripes of the plurality of data stripes that would be incomplete due to the smaller DSD storage capacity of the replacement DSD; assign a replacement strip size for the incomplete data stripes to each DSD of the plurality of DSDs other than the replaced DSD and the replacement DSD, wherein the replacement strip size is based at least in part on a portion of the total replacement storage capacity that is contributed by the DSD storage capacity of the respective DSD; and store the incomplete data stripes across the plurality of DSDs other than the replaced DSD and the replacement DSD such that for each incomplete data stripe, each DSD stores a different replacement portion of the incomplete data stripe having the replacement strip size assigned to the DSD.
 5. The data storage system of claim 4, wherein in identifying incomplete data stripes of the plurality of data stripes, the controller is further configured to determine the number of incomplete data stripes by dividing the difference between the DSD storage capacity of the replaced DSD and the DSD storage capacity of the replacement DSD by a data size for each of the plurality of data stripes.
 6. The data storage system of claim 1, wherein: the plurality of DSDs stores a plurality of data stripes across the plurality of DSDs; and the controller is further configured to, responsive to one of the plurality of DSDs being replaced by a replacement DSD having a DSD storage capacity greater than the DSD storage capacity of the replaced DSD: assign a new strip size to each DSD of the plurality of DSDs including the replacement DSD based at least in part on a portion of a new total storage capacity for the plurality of DSDs that is contributed by the DSD storage capacity of the respective DSD; receive data for storage in a new data stripe; and store the new data stripe across the plurality of DSDs including the replacement DSD such that each DSD stores a different portion of the new data stripe having the new strip size assigned to the DSD.
 7. The data storage system of claim 1, wherein the controller is further configured to, responsive to one or more new DSDs being added to the plurality of DSDs: assign a new strip size to each new DSD of the one or more new DSDs based at least in part on a portion of a new total storage capacity for the one or more new DSDs that is contributed by a DSD storage capacity of the respective new DSD; receive data for storage in a new data stripe; and store the new data stripe across the one or more new DSDs such that each new DSD stores a different portion of the new data stripe having the new strip size assigned to the new DSD.
 8. The data storage system of claim 1, wherein the plurality of DSDs includes at least one Solid-State Drive (SSD).
 9. The data storage system of claim 1, wherein the controller is further configured to assign a strip size to each DSD of the plurality of DSDs based at least in part on a DSD storage capacity contributed by the DSD to the total storage capacity.
 10. A method of operating a data storage system including a plurality of Data Storage Devices (DSDs) collectively having a total storage capacity available for storing user data among the plurality of DSDs, with each DSD of the plurality of DSDs having a DSD storage capacity that contributes to the total storage capacity of the plurality of DSDs, the method comprising: determining a weight for each DSD of the plurality of DSDs based on a percentage of the total storage capacity that is contributed by the DSD storage capacity of the respective DSD; assigning a strip size to each DSD of the plurality of DSDs based on the determined weight for the respective DSD, including: assigning a first strip size to a first DSD of the plurality of DSDs based at least in part on a first DSD storage capacity contributed by the first DSD to the total storage; and assigning a second strip size to a second DSD of the plurality of DSDs based at least in part on a second DSD storage capacity contributed by the second DSD to the total storage capacity, wherein: the second DSD storage capacity contributed by the second DSD differs from the first DSD storage capacity contributed by the first DSD, and the second strip size assigned to the second DSD differs from the first strip size assigned to the first DSD; receiving data for storage in a data stripe across the plurality of DSDs; and storing the data stripe across the plurality of DSDs such that each DSD of the plurality of DSDs stores a different portion of the data stripe, wherein: the first DSD stores a first portion of the data stripe having the first strip size, and the second DSD stores a second portion of the data stripe having the second strip size.
 11. The method of claim 10, wherein the method further comprises determining the plurality of DSDs from a larger set of DSDs by: pairing each of one or more DSDs of the larger set with another DSD of the larger set that has the closest DSD storage capacity available for storing user data; and for each pair of DSDs: setting a first DSD of the pair as a DSD of the plurality of DSDs; and setting the other DSD of the pair as a mirroring DSD for storing a copy of user data stored on the first DSD.
 12. The method of claim 10, wherein: the data storage system further includes at least one mirroring DSD for storing a copy of user data stored on a respective mirrored DSD of the plurality of DSDs; and the method further comprises determining the DSD storage capacity contribution for each mirrored DSD of the plurality of DSDs using a mirroring DSD storage capacity of the mirroring DSD responsive to the mirroring DSD storage capacity being less than the DSD storage capacity of the mirrored DSD.
 13. The method of claim 10, wherein: the plurality of DSDs stores a plurality of data stripes across the plurality of DSDs; and the method further comprises, responsive to one of the plurality of DSDs being replaced by a replacement DSD having a DSD storage capacity less than the DSD storage capacity of the replaced DSD: determining a difference between the DSD storage capacity of the replaced DSD and the DSD storage capacity of the replacement DSD, wherein the total storage capacity is reduced to a total replacement storage capacity for storing user data among the plurality of DSDs other than the replaced DSD and the replacement DSD; identifying incomplete data stripes of the plurality of data stripes that would be incomplete due to the smaller DSD storage capacity of the replacement DSD; assigning a replacement strip size for the incomplete data stripes to each DSD of the plurality of DSDs other than the replaced DSD and the replacement DSD, wherein the replacement strip size is based at least in part on a portion of the total replacement storage capacity that is contributed by the DSD storage capacity of the respective DSD; and storing the incomplete data stripes across the plurality of DSDs other than the replaced DSD and the replacement DSD such that for each incomplete data stripe, each DSD stores a different replacement portion of the incomplete data stripe having the replacement strip size assigned to the DSD.
 14. The method of claim 13, wherein in identifying incomplete data stripes of the plurality of data stripes, the method further comprises determining the number of incomplete data stripes by dividing the difference between the DSD storage capacity of the replaced DSD and the DSD storage capacity of the replacement DSD by a data size for each of the plurality of data stripes.
 15. The method of claim 10, wherein: the plurality of DSDs stores a plurality of data stripes across the plurality of DSDs and the method further comprises, responsive to one of the plurality of DSDs being replaced by a replacement DSD having a DSD storage capacity greater than the DSD storage capacity of the replaced DSD: assigning a new strip size to each DSD of the plurality of DSDs including the replacement DSD based at least in part on a portion of a new total storage capacity for the plurality of DSDs that is contributed by the DSD storage capacity of the respective DSD; receiving data for storage in a new data stripe; and storing the new data stripe across the plurality of DSDs including the replacement DSD such that each DSD stores a different portion of the new data stripe having the new strip size assigned to the DSD.
 16. The method of claim 10, wherein the method further comprises, responsive to one or more new DSDs being added to the plurality of DSDs: assigning a new strip size to each new DSD of the one or more new DSDs based at least in part on a portion of a new total storage capacity for the one or more new DSDs that is contributed by a DSD storage capacity of the respective new DSD; receiving data for storage in a new data stripe; and storing the new data stripe across the one or more new DSDs such that each new DSD stores a different portion of the new data stripe having the new strip size assigned to the new DSD.
 17. The method of claim 10, wherein the plurality of DSDs includes at least one Solid-State Drive (SSD).
 18. The method of claim 10, further comprising assigning a strip size to each DSD of the plurality of DSDs based at least in part on a DSD storage capacity contributed by the DSD to the total storage capacity.
 19. A controller for a data storage system including a plurality of Data Storage Devices (DSDs) having a total storage capacity available for storing user data among the plurality of DSDs with each DSD of the plurality of DSDs having a DSD storage capacity that contributes to the total storage capacity of the plurality of DSDs, the controller comprising: an interface for communicating with the plurality of DSDs; and a processor configured to: determine a weight for each DSD of the plurality of DSDs based on a percentage of the total storage capacity that is contributed by the DSD storage capacity of the respective DSD; assign a strip size to each DSD of the plurality of DSDs based on the determined weight for the respective DSD, including: assign a first strip size to a first DSD of the plurality of DSDs based at least in part on a first DSD storage capacity contributed by the first DSD to the total storage capacity; and assign a second strip size to a second DSD of the plurality of DSDs based at least in part on a second DSD storage capacity contributed by the second DSD to the total storage capacity; wherein: the second DSD storage capacity contributed by the second DSD differs from the first DSD storage capacity contributed by the first DSD, and the second strip size assigned to the second DSD differs from the first strip size assigned to the first DSD; receive data for storage in a data stripe across the plurality of DSDs; and store the data stripe across the plurality of DSDs such that each DSD of the plurality of DSDs stores a different portion of the data stripe, wherein the first DSD stores a first portion of the data stripe having the first strip size and the second DSD stores a second portion of the data stripe having the second strip size.
 20. The controller of claim 19, wherein the processor is further configured to assign a strip size to each DSD of the plurality of DSDs based at least in part on a DSD storage capacity contributed by the DSD to the total storage capacity.
 21. An apparatus for operating a data storage system including a plurality of Data Storage Devices (DSDs) having a total storage capacity available for storing user data among the plurality of DSDs with each DSD of the plurality of DSDs having a DSD storage capacity that contributes to the total storage capacity of the plurality of DSDs, the apparatus comprising: means for determining a weight for each DSD of the plurality of DSDs based on a percentage of the total storage capacity that is contributed by the DSD storage capacity of the respective DSD; means for assigning a strip size to each DSD of the plurality of DSDs based on the determined weight for the respective DSD, including: means for assigning a first strip size to a first DSD of the plurality of DSDs based at least in part on a first DSD storage capacity contributed by the first DSD to the total storage capacity; and means for assigning a second strip size to a second DSD of the plurality of DSDs based at least in part on a second DSD storage capacity contributed by the second DSD to the total storage capacity; wherein: the second DSD storage capacity contributed by the second DSD differs from the first DSD storage capacity contributed by the first DSD, and the second strip size assigned to the second DSD differs from the first strip size assigned to the first DSD; means for receiving data for storage in a data stripe across the plurality of DSDs; and means for storing the data stripe across the plurality of DSDs such that each DSD of the plurality of DSDs stores a different portion of the data stripe, wherein the first DSD stores a first portion of the data stripe having the first strip size and the second DSD stores a second portion of the data stripe having the second strip size. 